The evaluation of the nutrient composition of feeds and foods has traditionally included an analysis of crude fat. Crude fat is primarily a measure of the triglyceride content of the food or feed and represents the more energy dense component. Fat is commonly extracted from feed and food with diethyl either or petroleum ether. Compounds other than fat are soluble in diethyl ether or petroleum ether but they represent minor components in relation to the energy contribution to the diet and generally fall in the category of lipids. The quantitative analysis of crude fat has traditionally been accomplished by the Soxhlet extraction technique (Quantitative Chemical Analysis, by Hamilton and Simpson). The current state of the art of fat analysis is described in, "Methods of Analysis for Nutritional Labeling". The standardized Soxhlet technique is detailed by the Association of Official Analytical Chemists in the AOAC Official Method 920.39. This Soxhlet technique involves placing an individual sample in a filter chamber. This filter chamber is then placed in the siphoning compartment. The heater boils the solvent, commonly petroleum ether, and passes the vapor into a condenser. The condenser condenses the vapor into a liquid, channels it into the filter chamber and siphoning compartment. The solvent is periodically siphoned back into the distilling flask after it reaches a certain level in the siphoning compartment. The distillation/extraction process is continued for four to sixteen hours. The fat content of the sample is then determined either by evaporating the solvent and measuring the remaining fat directly or indirectly by weighting the weight loss of the sample contained in the filter chamber. The filter chambers that are commonly used are thimble shaped filter paper. Glass filter chambers with fritted glass filters and fritted Alundum thimbles are also used.
As described above, the prior art for crude fat analysis that is currently being used by regulatory laboratories, industry and academia involves individual analysis based on the traditional Soxhlet technique.
Apparatus designed to expedite the Soxhlet extraction process and improve the manual efficiency of the extraction process are described in U.S. Pat. No. 4,184,961. Improvements in the rate of extraction and solvent penetration of the sample matrix have been achieved by increasing the temperature and pressure of the extracting solvent as taught by U.S. Pat. No. 4,265,860. These instruments have the same limitation as the standard Soxhlet process of dealing with individual samples individually throughout the analysis. These instruments deal with individual samples in multiple setups and semi-automate or automate individual steps such as extraction, rinsing and solvent evaporation. These instruments can only process a limited number of samples since they deal with samples individually (up to twelve), and require costly equipment when calculated on a per sample basis.
In all of the systems described above, the samples are processed individually in order to yield a unique value for each sample. This requirement of individual sample processing limits the efficiency of the analysis and increases the cost of the instrument by requiring a replicate of the apparatus for each sample capable of being analyzed by the instrument.
U.S. Pat. No. 5,370,007 is directed to a Fiber Analysis System in which a sample of a feedstuff or food of a predetermined weight is sealed in a filter bag with selected porosity which recovers the fiber components while allowing the removal of the detergent soluble components of the sample. The fiber analysis taught by the '007 patent is accomplished by exposing the sample to an aqueous detergent solution (polar solvent) under heated conditions for a time sufficient to remove substantially all soluble solids from the feed while retaining the fiber components within the filter bag. The preparation of samples for analysis requires that the samples be ground to a fine particle size in order to ensure a representative aliquot. The sample grinding process fractures and fragments the different components of the feed differently. Non-fiber components such as non-structural carbohydrates, sugars, proteins, and minerals fracture into much finer particles than the fiber components. Because the large majority of fine particles are not fiber, their passage through the fiber filter media causes no error. Therefore the filtration media used in these filter bags benefits from the surface tension of the aqueous solution, and from the fact that very fine particles are soluble and do not need to be retained. To ensure accurate fiber results, only retention of particles larger than 25 microns is required for the filter media.
The significant differences between fiber analysis of the prior art and fat analysis of the present invention include: retention vs extraction of the analyte; the use of aqueous solutions vs. organic solvents; and the retention of coarse particle vs fine particle; 25 micron vs &lt;4 micron filter media. These differences will become more apparent with a reading of the detailed description of the invention.